Abstract:In this study the results of PSHA deaggregation for 5%-damped 0.2, 0.5, 2 and 4 s spectral accelerations, corresponding to Mean Return Periods (MRPs) of 50 and 475 yr for Karaj city was presented. The aim of this paper is to quantify the dominant events that have the most contribution on ground-motion exceedance from the above mentioned hazard levels. The scenario earthquakes are characterized by bins of Magnitude (M) and source-to-site distance (R). The results reveal that for Karaj city, the hazard is mainly controlled by near active fault.

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The earthquake hazard is most important title in seismic design of buildings. One of ways to know this hazard is to know where the earthquake boundary is. Moreover, understanding of the future earthquakes location, can help to modify the seismic hazard maps. The bvalues, is the effective parameter on future earthquake positioning. This study was conducted to variations of b-values in the Gutenberg-Richter relation were examined for tectonic earthquakes in the NW of Iran. Earthquake dates for this area are given from the ISC, NEIC and Engdahl catalogues for a period of 735 to 2017 were used for analysis. We separated earthquake catalogue in part 1(before 2000) and Part 2 (all events). Delineated zone from b-value distribution map in catalogue Part 1, showed us five seismic gap region (area A to E) with a potential for the occurrence of earthquakes in the near future. The results of Part 2 showed that in areas A, B and C the future earthquake had happened. Therefore, we are waiting for last seismic events in the D and E areas. This "seismic gaps" is a potential threat to the surrounding regions, such as the Nakhichevan and Rasht city.

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This study presents evidence for the existence of a vast and ancient lake that occupyed a large area of central Iran during the Holocene. The northwestern fringe of the lake, located in the southeast of Tehran, was chosen as the study area. Remains of a Paleo Lake scarp was studied using aerial photographs, Quick Bird satellite imagery, and topographic maps. Furthermore, archeological sites within the region were identified and located, and evidence for the lake was obtained through correlation of these data. Eight shorelines were identified between 1100 -950 m above sea level, with a depth of 3 -15 m, and a 43 km in lenght. The results indicated that the active Quaternary faults named North Rey, Kahrizak, and South Rey are in fact the three main topographic levels of the paleo lake and from now on they cannot be considered as the faults. Soil granulation and thin sections showed the presence of non-compacted lake sediments. Results revealed a remarkable association between the location of ancient settlements and altitude of the identified paleo shorelines. All settlements older than 5,000 years were located at 1,000 m. Certainly, the past climate of this region was very different from its contemporary one. Dating studies will provide valuable information about the exact age of the Paleo -Lake and paleo climate changes.

Takavar and Ebtehaj tunnels as part of Haraz highway are located in southwestern Damavand mount. Statistics show enormous financial and human damages in this route because of rockfall. Geological and topographical conditions, caused to the intensity of rockfall, because most of heights in this area covered by Damavand Trachyandesitic lava flows. In this study Rockfall Analyst (RA) software used to analysis risk modeling of rockfall in three-dimensional. In such a model, the spatial distribution of frequency, height velocity and energy of falling or rolling rocks are calculated. Then the layers in the same velocity, energy and height and the weight, were analyzed and finally 9 risk-prone regions were identified. However, except one of them, other areas need engineering solutions to drop the risk of rockfall.

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Awareness of seismicity, is the earliest requirement in seismic design of Dam constructions. This article is devoted to study on Seismotectonic and seismicity and also seismic risk analysis of the Baychebaq reservoir dam. These studies involve detecting seismic sources and assessing seismicity parameters. According to the studies, Peak Ground Acceleration (PGA) is 0.1 gal. This PHA may be related to there activation process of Takhte Soleiman which can produce an event around 6.8 Ms in the distance of 20 km from Baychebaq dam. According to the changes of Uniform Hazard Spectrum (UHS), Spectral acceleration parameter increases from period of 0 (0.03 gal) to a period of 0.175 (0.1 gal) and then reduced slightly. Based on the results, the controlling earthquake has a magnitude of 6.1 and 6.5 Mw at a period of 0 for return periods of 475 and 2475 years.